1. Field of the Invention
This invention relates to an air core current transformer, and more particularly, it pertains to a toroidal winding of a dielectric substrate folded to form a cylindrical toroidal core.
2. Description of the Prior Art
Electronic watthour meters have been developed to replace the existing electromechanical meters to derive the advantages of greater accuracy, lower construction cost, and ease of interfacing with associated electronic equipment including time-of-day metering devices. Such devices are disclosed in U.S. Pat. No. 4,283,772, "Programmable Time Registering AC Electric Energy Meter Having Electronic Accumulator And Display".
A type of electronic watthour meter is disclosed in U.S. Pat. No. 4,413,230, for "Electric Energy Meter Having A Mutual Inductance Current Transducer", which employs a toroidal coil. For an electronic watthour meter to be immune to the effects of external magnetic fields that might result from currents flowing in conductors in the vicinity of the meter, it is necessary that the cross-section of the coil be constant, that is, exhibit the same cross-sectional area at any angular position, and that the turns be equally spaced. In addition, due to size limitations imposed by the meter base, the required coil is relatively long compared to the diameter. The disadvantage of such a coil is that it is costly to make by ordinary winding techniques used for mass production.